Transferring and fixing system and method using a guided conveyor section and a free conveyor section

ABSTRACT

In a method and system for transfer printing of an electrostatic recharge toner image from an intermediate carrier onto a recording medium and for fixing of the transfer-printed toner image onto the recording medium, the recording medium lying on an electrostatically-chargeable conveyor belt and adhered thereto by electrostatic forces is transported through a transfer printing region and subsequently along a guided transport section. The recording medium is conveyed to a fixing device. The guided transport section is arranged in a transport unit and the fixing device is arranged in a fixing unit which are independent of one another. The fixing unit has at least one wall designed to hinder a heat transfer from the fixing unit to the transport unit.

BACKGROUND

The disclosed embodiment generally relates to a device and a method fortransfer printing of an electrostatically charged toner image from anintermediate carrier of an electrographic printer or copier onto arecording mediums and fixing of the transfer-printed toner image ontothe recording medium.

In electrographic printers or copiers, the transfer of a toner imagefrom an intermediate carrier (for example a photoconductor drum or aphotoconductor ribbon) onto a recording medium is designated as transferprinting. The section of the printing or copying device at which theintermediate carrier and the recording medium are brought into contactwith one another is designated as a transfer printing region. In thetransfer printing region, the intermediate carrier (meaning, forexample, the generated surface of a photoconductor drum) and therecording medium move in the same direction with the same speed, whilethe toner is transferred from the intermediate carrier onto therecording medium. A print image of high quality can only be achieved onthe recording medium when a uniform contact between recording medium andintermediate carrier is produced in the transfer printing region andwhen the recording medium and the intermediate carrier actually movewith exactly the same speed in the transfer printing region.

In known printing or copying devices, the recording media aretransported with transport rollers in the transfer printing region andeffected on the side facing away from the intermediate carrier with acharge whose polarity sign is opposite to the charge of the toner imageand of the intermediate carrier. The recording medium is therebyattracted by the intermediate carrier and transported through thetransfer printing region adhering to this; at the same time the chargeof the recording medium effects the transfer of the charged tonerparticles from the intermediate carrier onto the recording medium. Uponleaving the transfer printing region, the recording medium is thendischarged with the aid of a discharge device with which it is loosenedfrom the intermediate carrier and transported to a fixing device.

A transfer printing device of this type is known from WO 98/58297 A1.This transfer printing device has a contact element to press therecording medium onto the intermediate carrier. From WO 98/18052, aprinter is known with two similar printing groups to which recordingmedia are supplied via an input section. The printed recording mediumare output via a common output section. An outlet channel is associatedwith the one printing group, via which outlet channel the recordingmedia that have been printed on one side by this printing group can bere-supplied to this printing group for printing of the back side. Arecording medium printed by the other printing group can be removed viathe outlet channel to the output section by bypassing the transferprinting transport path of the first-cited printing group.

Further prior art is to be learned from the documents DE 199 56 505 A1,DE 43 24 148 C2, U.S. Pat. No. 5,666,622 A, US 2002/057933 A1, DE 40 39158 A1, JP 2002-268 301 A, DE 77 36 767 U1 and DE 34 06 290 C2.

During the transport of a recording medium from the transfer printingregion to the fixing device, its printed side may not be contactedbecause the not-yet-fixed toner image would otherwise be smeared. Inconventional devices for transport of the printed recording medium, avacuum table is therefore typically used in which the recording mediumis held on a transport ribbon via suction pressure. In the fixingdevice, the recording medium is guided between two rollers whosegenerated surfaces abut closely to one another along a surface line andform a roller contact region or transport gap. The roller contact regionor transport gap is also often designated in the German literature withthe English term “nip”. Of the two rollers at least one is heated, andthe toner image is affixed on the recording medium via pressure andheat.

Upon entrance of the recording medium into the roller contact region,the fixing rollers perform an additional milling task, whereby therecording medium is temporarily braked (this experiences a suddenjarring) that is in the direction opposite the transport direction. Thedistance between fixing rollers and transfer printing region is oftenless than the length of the longest recording medium to be printed incompactly designed printers or copying devices and in particular indevices with two printing groups. By the “length” of the recordingmedium, what is always meant in the following is the dimension of therecording medium in the transport direction, thus the length of theedges of the recording medium that are arranged parallel to thetransport path. Given a rectangular recording medium, these do notnecessary have to be the “lengthwise edges”, but rather can also be itstransverse edges, namely when it is printed in the landscape format.

When the distance between the transfer printing region and the fixingrollers is shorter than the length of the recording medium, it can occurthat the leading edge of the recording medium experiences a jarring inthe roller contact region while the recording medium is still beingprinted at a rear section. In the event that this jarring transfer tothe rear section, this leads to a smearing of the print image which isunacceptable.

SUMMARY

It is an object to specify a device and a method with which a printimage of high quality can be generated given a compact design.

In a method and system for transfer printing of an electrostaticrecharge toner image from an intermediate carrier onto a recordingmedium and for fixing of the transfer-printed toner image onto therecording medium, the recording medium lying on anelectrostatically-chargeable conveyor belt and adhered thereto byelectrostatic forces is transported through a transfer printing regionand subsequently along a guided transport section. The recording mediumis conveyed to a fixing device. The guided transport section is arrangedin a transport unit and the fixing device is arranged in a fixing unitwhich are independent of one another. The fixing unit has at least onewall designed to hinder a heat transfer from the fixing unit to thetransport unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the components of anelectrographic printing or copying device participating in the imagegeneration, with a conventional device for transfer printing of a tonerimage from an intermediate carrier onto a recording medium and fixing ofthe transfer-printed toner image onto the recording medium;

FIG. 2 is a schematic representation of a recording medium givenentrance into the roller contact region of two fixing rollers;

FIG. 3 shows the device for transfer printing and fixing from FIG. 1with a recording medium with low rigidity;

FIG. 4 shows the device for transfer printing and fixing from FIG. 1with a recording medium with high rigidity;

FIG. 5 is a schematic representation of the components of anelectrographic printing or copying device participating in the imagegeneration, with a device for transfer printing of a toner image from anintermediate carrier onto a recording medium and fixing of thetransfer-printed toner image onto the recording medium;

FIG. 6 shows the device for transfer printing and fixing from FIG. 5with a recording medium with high rigidity; and

FIG. 7 is a section view of a transport unit and a fixing unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the preferred embodimentillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, such alterations andfurther modifications in the illustrated device, and/or method, and suchfurther applications of the principles of the invention as illustratedtherein being contemplated as would normally occur now or in the futureto one skilled in the art to which the invention relates.

A compact design of the device inevitably leads to a small distancebetween transport ribbon and the fixing device. Due to the spatialproximity, the conveyor belt is likewise heated by the heat necessaryfor fixing, whereby it can deform and thereby be impaired with regard toits function. Moreover, given heating of the conveyor belt the dangerexists that toner located on it begins to melt and adheres on theconveyor belt.

The guided transport section is arranged in the preferred embodiment ina transport unit and the fixing device is arranged in the preferredembodiment in a fixing unit that are used independently of one anotherin the printer or copier and can be removed from these. Via thestructural separation of the two units, no heat can be transferred overcommon components, for example circuit boards.

The fixing unit thus has a wall designed as a hollow chamber profilethat offers a good heat insulation. In a particularly advantageousdevelopment, the hollow chamber profile has openings through which aircan be drawn for cooling of the transport unit.

In the device and a method according to an advantageous development ofthe preferred embodiment, the recording medium lying on anelectrostatically chargeable conveyor belt and adhered to this viaelectrostatic forces is transported along a subsequent guided transportsection and conveyed, via a free transport section (subsequent to theguided transport section) in which the recording medium can freely arch,to a fixing device in which the recording medium is again guided in afixed manner.

A “free transport section” designates in this document a transportsection on which the recording medium is freely arched, and thus canform a wave or a buckle, whereby the distance between its front and rearedge is shortened. By forming an arch or wave, the shock that is exertedon its front edge upon entry of the recording medium into the rollercontact region of the fixing roller can be absorbed.

The developed device or method thus effectively prevents a smearing ofthe print image. On the one hand, a stronger adhesion can be achievedwith the aid of an electrostatically-chargeable conveyor belt than witha vacuum table, such that the section of the recording medium located inthe guided transport section can be not-so-lightly braked by the shock.On the other hand, the shock can be absorbed by the possibility for waveformation in the free transport section.

A secure guidance of the recording medium in the guided transportsection assumes a sufficient electrostatic charge of the conveyor beltthat is maintained over the entire length of the guided transportsection. The conveyor belt therefore preferably has a specific volumeresistance of between 10¹¹ and 10¹⁵ Ωcm. In a particularly advantageousembodiment, the conveyor belt is significantly comprised ofpolyvinylidenfluoride (PVDF).

In spite of a compact design, the guided transport section must be longenough to ensure a sufficiently safe guidance that precludes a smearingof the print image in the transfer printing region. The length L₁ of theguided transport section is preferably between 100 and 210 mm.

The length L₂ of the free transport section must be large enough that awave with a not-too-slight curvature can form to absorb the shock. L₂ ispreferably ⅓ of the length of the shortest recording medium to beprinted. A good wave formation results given a length of L₂ between 80and 130 mm.

The components of an electrographic printer participating in the imagegeneration are schematically shown in FIG. 1. The main features of theelectrographic printing or copying are explained briefly with regard tothese in the following.

A photoconductor drum 10 is shown in cross-section in FIG. 1 whoseperipheral area is coated with a photosemiconductor, for examplearsentriselenide (As₂Se₃). Such a photosemiconductor has a high darkresistance that, however, decreases given sufficient exposure. Thephotoconductor drum 10 rotates in the direction indicated with the arrow12. Its photoconductor layer is thereby initially electrostaticallycharged with the aid of what is known as a charge corotron 14. Viarotation of the photoconductor drum 10, the charged section arrives at acharacter generator 16 with a light source 18 (an LED comb in FIG. 1)with which the photoconductor drum 10 is exposed. The electricalresistance of the photoconductor drum layer drops at the exposedlocations and the charge discharges. Image points of a latent chargeimage are thus generated on the photoconductor drum.

Given a further rotation of the photoconductor drum 10, the latentcharge image arrives at a developer station 20 from whichtriboelectrically-charged toner is transferred (with the aid of asuitable electrical field) from a developer roller 22 onto the exposedlocations (what is known as “dark writing”) or unexposed locations (whatis known as “light writing”) of the photosemiconductor. The charge imagelocated on the photoconductor drum 10 is thus inked with toner, i.e.developed. The toner image is subsequently transferred onto a recordingmedium, for example a sheet of paper 24. The photoconductor drum 10 istherefore generally designated as an intermediate carrier.

The sheet 24 is transported into the transfer printing region 28 withthe aid of transport rollers 26. The section at which the photoconductordrum 10 and the sheet 24 come in contact with one another and the tonerimage is transferred onto the sheet 24 is designated with “transferprinting region”. In the conventional device shown in FIG. 1 fortransfer of the toner image from the photoconductor drum 10 onto thesheet 24, the latter is sprayed (with the help of what is known as atransfer corotron 30) on its underside with charge that is opposite tothe charge of the toner. The sheet 24 thereby adheres to thephotoconductor drum 10 and the toner is transferred onto the sheet 24via the electrostatic adhesion.

To separate the sheet 24 from the photoconductor drum 10, it issubsequently discharged again with the aid of an alternating currentcorotron 32, such that the electrostatic adhesion forces disappear andthe sheet 24 shears from the photoconductor drum 10 due to its rigidity.The printed sheet 24 is then transported into a fixing device 3 via avacuum table 34. Toner remaining on the photoconductor drum 10 after thetransfer printing is removed by a cleaning unit 50.

The fixing device 36 has two rollers, a heated fixing roller 38 and apressure roller 40 that presses against the fixing roller 38 and, withthis, forms a roller contact region 44. The rollers 38 and 40 rotate ina direction (characterized with arrows 42) with a circumferentialvelocity V_(f). For fixing, the sheet is guided along the transport path46 through the roller contact region 44. All components participating intransfer printing and fixing are situated in a common structural unit48.

The device from FIG. 1 is kept so compact that the distance betweentransfer printing region 28 and fixing device 36 is smaller than thelength of the longest recording medium to be printed. This means thatthe leading edge of such a recording medium already enters into theroller contact region 44 while a rear section of the same is still beingprinted in the transfer printing region 48.

In FIG. 2, the fixing device 36 is shown in which the leading edge ofthe recording medium 24 enters into the roller contact region 44 formedby the fixing roller 38 and the pressure roller 40. As is to be seen inFIG. 2, the rollers 38 and 40 are thereby deformed. Upon entering intothe roller contact region 44, the leading edge of the sheet istemporarily braked and experiences a shock with an impact force F_(s).The impact force F_(s) is opposite to the movement direction of thesheet 24 and is represented in FIG. 2 by a force arrow.

In FIG. 3, for reasons of clarity only those components of theconventional arrangement of FIG. 1 are shown that are participating inthe transfer printing and the fixing. Furthermore, a sheet 24′ is shownin FIG. 3 whose leading edge directly enters into the roller contactregion 44 of the rollers 38 and 40 and thus experiences the impact forceF_(s) just described while a rear section of the sheet 24′ is stilllocated in the transfer printing region 28.

In the snapshot shown in FIG. 3, the impact force F_(s) leads toformation of a wave 52 in the sheet 24′. In this context, what is meantwith “wave” is a curved section of the sheet 24′ that deviates from theactual provided transport path. The sheet 24′ of FIG. 3 has lowerrigidity, such that only a slight force is required in order to curvethe sheet into a wave 52. Moreover, the tendency of the sheet 24′ toshear away from the vacuum table 34 upon formation of the wave 34 is lowdue to the low rigidity of the sheet 24′. The suction force of thevacuum table 34, which is shown in FIG. 3 by the arrow pointingperpendicularly downwards, is sufficient to prevent a shearing of thesheet 24′ from the vacuum table 34. The rear section of the sheet 24′ isthus guided on the vacuum table and the impact force F_(s) is nottransferred until the transfer printing region.

The same components are shown in FIG. 4 as in FIG. 3, only in FIG. 4 asheet 24′ with a higher rigidity is transported. Due to the higherrigidity of the sheet 24″, in the representation of FIG. 4 no wave isformed; instead of this the sheet 24″ shears from the vacuum table 34.The sheet 24″ is nearly stretched, such that the impact force F_(s) istransferred up to the transfer printing region 28, whereby the printimage is smeared.

The specified problem of the print image smearing can only be avoidedwith great additional effort in the conventional device of FIGS. 1, 3and 4. For example, the shock can be largely attenuated via a suitablespeed control of the fixing rollers 38 and 40 that is triggered by theinfeed of the leading sheet edge into the roller arrangement. However,the control must account for the thickness of the paper on which theimpact force F_(s) is dependent. This requires an elaborate sensortechnology with a corresponding regulation device. Given sheets withhigh inherent rigidity and large thickness, a print image smearingcannot be completely prevented even with such a controller. In thiscase, the pressure force of the rollers upon entrance of the leadingsheet edge into the roller contact region 44 must be temporarilyreduced, which in turn requires a high mechanical effort andadditionally impairs the fixing quality in the region of the leadingedge.

An arrangement of components participating in the image generation thatis identical in significant parts is schematically shown in FIG. 5 as inFIG. 1, in which is shown, however, a device for transfer printing andfixing according to a development of the preferred embodiment. Thedevice has a transport ribbon 54 that is guided around a first roller56, a second roller 58, a third roller 60 and a positioning roller 62.In the representation of FIG. 5, the conveyor belt 54 is drivencounterclockwise by the first roller 56 with a circumferential speed v₀that coincides with the tangential speed of the generated surface of thephotoconductor drum 10. The third roller 60 is pre-stressed with aspring 64, such that it exerts a tensile stress on the conveyor belt 54.The positioning roller 62 is arranged between the first roller 56 andthe transfer printing region 28 and positions the conveyor belt 54outwards relative to an alignment 66 of the first and second roller 56,58. The positioning roller 62 provides for a narrow arrangement of theconveyor belt 54 on the photoconductor drum 10, in that the conveyorbelt loops around the photoconductor drum in the transfer printingregion, i.e. contacts the generated surface of the photoconductor drumover a certain angle range.

A cleaning device 68 is arranged below the conveyor belt 54. Thecleaning device 68 has a blade 70 that is arranged transverse to therunning direction of the conveyor belt 54 and is arranged abutting thisand a toner capture reservoir 72 into which toner abraded from theconveyor belt 54 by the blade 70 falls.

A blade-like element 74 that is connected with a voltage source 76(schematically shown) and serves to charge the transport ribbon 54 abutson the side of the conveyor belt 54 facing away from the photoconductordrum 10. The conveyor belt 54 with the associated rollers 56, 58, 60 and62, the cleaning device 68, and the contact blade 74 are structurallyintegrated into a transport unit 78 that is represented by a frameworkshown dashed in the schematic representation of FIG. 5.

In FIG. 5, a fixing device 36 is shown that does not significantlydiffer from those of FIGS. 1, 3 and 4, however is integrated into astructurally independent fixing unit 80 that is likewise schematicallyshown by a framework shown in dashed lines. A guide plate 82 alsobelongs to the fixing unit 80. A discharge device 84 is arranged abovethe first roller 56.

The function of the device is explained in detail in the following withreference to FIG. 5. The conveyor belt 54 is charged via the contactblade 74 to an electrostatic potential of some kilovolts relative to aground potential, whereby the polarity sign of the charge of theconveyor belt 54 is different from the polarity sign of the charge ofthe toner image on the photoconductor drum 10. A recording medium 24 isconveyed onto the conveyor belt 54 with the aid of transport rollers 26in the region of the second roller 58 and electrostatically adheres tothis transport band 54. In the transfer printing region, the conveyorbelt 54 loops around the photoconductor drum 10 at a certain angle rangeand thereby produces a uniform contact between the sheet 24 lying on theconveyor belt 54 (and adhering thereto) and the photoconductor drum 10.

The conveyor belt 54 has a specific volume resistance between 10¹¹ and10¹⁵ Ωcm, such that the section between the first roller 56 and thetransfer printing region 28 retains a sufficient electrostatic charge inorder to hold the sheet 24 on it via electrostatic forces. The transportpath between the transfer printing region 28 and the first roller 56 istherefore called a “guided transport section” in the following. Aparticularly good guidance results given a conveyor belt that issignificantly comprised of polyvinylidenfluoride (PVDF), has a specificvolume resistance of 8×10¹² Ωcm and a thickness of 150 μm.

The first roller 56 is an antistatic roller made from silicon with aspecific volume resistance of 10⁸ Ωcm and is therefore suited todissipate a larger part of the charge of the conveyor belt 54 away fromthis at the end of the guided transport section. The first roller 56 hasa diameter of less than 28 mm, such that the conveyor belt 54 isrelatively significantly curved on said roller 56 and the sheet 24easily shears from the conveyor belt 54 guided around the first roller56.

Depending on the charge strength and composition of the conveyor belt54, it can be advantageous to already have dissipated a certain chargequantity from the conveyor belt 54 at the positioning roller 62. Thequantity of the charge dissipated at the drawing roller can beinfluenced by its material, for example the choice between metal andplastic.

During the guided transport section, the transfer-printed butnot-yet-fixed toner is held on the sheet 24 by the electrostaticattraction of the conveyor belt 54. After the shearing of the sheet 24from the conveyor belt 54 in the region of the first roller 56, thisattraction is lacking and the similarly-charged toner particles tend torepel one another and accumulate in conductive parts located in thesurroundings and contaminate these. In order to prevent this, uponshearing of the sheet 24 from the conveyor belt 54, the toner located onthe sheet 24 is discharged with the aid of the discharge device 84.

The sheet sheared from the transport ribbon 24 is guided over the guideplate 82 into the fixing unit 80 and there is fixed. Outside of gravity,no forces affect the sheet 24 between the first roller 56 and the rollercontact region 44. This section is therefore called a free transportsection in the following. In the free transport section, the sheet 24has the possibility to form a wave, and thus to absorb the describedimpact force F_(s).

FIG. 6 is a snapshot in which the leading edge of a sheet 24″ enters inthe roller contact region 44 while a rear section of the sheet 24″ isstill being printed in the transfer printing region 28. Although thesheet 24″ is the same sheet as in FIG. 4, here the shock is nottransferred into the transfer printing region 28; rather, the sheet 24″remains adhered to the conveyor belt 54 in the guided transport sectionwhile a wave forms in the free transport section.

Two reasons can be cited for the better behavior in the device of FIG. 6relative to the device of FIG. 4. On the one hand, with the conveyorbelt 54 presented here a clearly higher adhesion force of the sheet 24″to the conveyor belt 54 can be achieved than with a vacuum table. Theadhesion forces between the sheet 24″ and the conveyor belt 54 arerepresented in FIG. 6 by the vertical force arrows pointing downwards.The adhesion force in the direction of the first roller 56 does in factdecrease with the charge density in the conveyor belt 54, but even inthe proximity of the first roller 56 it is large enough in order toprevent a shearing of the sheet 24″. Even if the wave should projectsomewhat into the guided transport section, the safe guidance in thetransfer printing region is not impaired since, first, the impact forceabates with the propagation of the wave and, second, the adhesion forceof the sheet 24″ to the conveyor belt 54 increases in the direction ofthe transfer printing region 28.

On the other hand, the free transport section in which the wave can formis clearly larger than the free section in the device of FIGS. 3 and 4,such that a flatter wave can form that has a lesser tendency to shearfrom the conveyor belt 54 than a more significantly curved wave.

In FIG. 6, the length of the guided transport section is designated withL₁ and the length of the free transport section is designated with L₂.Given a compact design, a certain, optimally smaller distance is aimedfor between the transfer printing region and the fixing device, i.e. acertain value for the sum of L₁ and L₂. A larger value for L₁, i.e. alonger guided transport section, has the advantage that the totalretention force that the sheet 24″ experiences is relatively large.However, a larger value for L₂ has the advantage that a flatter wave canform, such that the shear forces are less. Given a desired value forL₁+L₂, an optimally ideal compromise must thus be found between L₁ andL₂.

However, by comparison with FIGS. 3 and 4, it is immediately clear thatas good a behavior never results with the conventional device with alikewise compact design (i.e. with an equal distance between transferprinting region 28 and fixing device 36) as with the device of FIGS. 5and 6. In the device from FIGS. 3 and 4, the guided region does notalready begin in the transfer printing region 28 because the sheet 24′or 24″ must be discharged in direct connection with the transferprinting so that it loosens from the photoconductor drum 10. Since thedischarge requires some time, however, at the same time a high processspeed is sought, and the belt discharge region cannot be selectedsignificantly shorter than as shown in FIGS. 3 and 4. The belt dischargeregion is thus lost, both for the retention of the sheet 24′ or 24″, andfor the wave formation.

A secure guidance of the sheet 24″ in the proximity of the transferprinting region 28 directly contributes to preventing a print imagesmearing. In the device from FIGS. 5 and 6, the retention force of thesheet 24″ on the conveyor belt 54 is strongest in proximity to thetransfer printing region 28, while in the device from FIGS. 3 and 4, thesheet 24′ or 24″ is not guided at all in proximity to the transferprinting region 28 because it still has to be discharged.

In order to achieve a secure guidance of the sheet, the length L₁ inFIG. 6 should amount to at least ⅓ of the length of the shortest sheetto be printed. By length, what is thereby meant is the dimension of thesheet in the transport direction, which can also by all means correspondto the shorter side given a rectangular sheet, namely when it is printedin portrait format. In the device from FIGS. 5 and 6, a secure guidancehas resulted without print image smearing given lengths of L₁ that arebetween 100 and 210 mm. The length L₂ may not be longer than the lengthof the shortest sheet to be printed (because otherwise this would not beguided at all in stretches) and should amount to at least ⅓ of thelength of the shortest sheet to be printed so that a sufficiently flatwave can form.

An advantageous wave formation can be supported via suitable selectionof the speed v_(f) with which the sheet 24″ is guided by rollers 38, 40of the fixing device. v_(f) is preferably between 97% and 100% of therotational speed v₀ of the conveyor belt 54.

The transport unit 78 and the fixing unit 90 are shown in a sectionrepresentation in FIG. 7. The use of two separate structural units hastwo large advantages. The one concerns the assembly, which is clearlyless elaborates with separate structural units. The transport unit 78must be very precisely adjusted relative to the photoconductor drum 10in order to ensure a good transfer printing, while the fixing unit 80does not have to be installed with such precision. When the devices fortransport and for fixing are combined in one common structural unit, asis the case with the structural unit 48 of FIG. 1, the entire structuralunit must be installed with high precision in order to ensure a transferprinting of high quality. However, since just the fixing device containsheavy components, the entire structural unit 48 is much heavier and moreunwieldy than the transport unit 78, and therefore also clearly moredifficult to precisely install.

The second advantage is that the heat radiated by the fixing roller 38does not so significantly heat the transport ribbon as would be the caseif the conveyor belt 54 and the fixing device 36 were arranged in acommon structural unit. This is of the highest importance since theconveyor belt 54 is deformed and loses its functionality due totoo-great heating.

The fixing unit 80 has a housing 86 that retains the heat radiated bythe fixing roller 38. In the side facing the transport unit 78, thehousing 86 has walls 88 and 90 that are designed as hollow chamberprofiles and therefore are good thermal insulators. The hollow chamberprofile 88 is aerated with a fan (not shown) and has openings 92 throughwhich air is drawn to cool the transport unit. The air current of thedrawn-in air is schematically represented by an arrow 94. In addition tothe cooling of the transport unit, the air intake also serves forcleaning of the transport unit of deposited toner particles.

The transport unit 78 and the fixing unit 80 can be advantageouslydesigned as plug-in modules.

The air taken up into the hollow chamber profile is filtered with theaid of an ozone filter (not shown) before it is dissipated into thesurroundings. In the illustrated embodiment, the fan (not shown) runsfor approximately a half-hour after the deactivation of the printer.

Although a preferred exemplary embodiment is shown and specified indetail in the drawings and the preceding specification, these should beviewed as purely exemplary and not as limiting the invention. It isnoted in this regard that only the preferred exemplary embodiment isshown and specified, and all variations and modifications should beprotected that presently or in the future lie within the scope ofprotection of the invention.

1-30. (canceled)
 31. A system for transfer printing of anelectrostatically charged toner image in an electrographic printing orcopying device, comprising: an intermediate carrier with anelectrostatically charged toner image thereon which transfers the tonerimage onto a recording medium at a transfer printing region; therecording medium lying on an electrostatically-chargeable conveyor beltand adhering thereto due to electrostatic forces and which transportsthe recording medium through said transfer printing region and along aguided transport section where it is conveyed to a fixing device; saidguided transport section being arranged in a transport unit and thefixing device being arranged in a fixing unit, said transport unit andfixing unit being used independent of one another and removable from theprinting or copying device; and said fixing unit having at least onewall designed as a hollow chamber profile which hinders a heat transferfrom the fixing unit to the transport unit.
 32. A system according toclaim 31 in which the at least one wall is designed as said hollowchamber profile.
 33. A system according to claim 32 in which the hollowchamber profile has openings through which air is drawn to cool thetransport unit.
 34. A system according to claim 33 wherein the openingsin the hollow chamber profile are arranged such that air is taken upinto the hollow chamber profile from an environment of the conveyorbelt.
 35. A system according to claim 33 in which an ozone filter isprovided to filter the air taken up into the hollow chamber profile. 36.A system according to claim 31 in which a fan is provided to draw theair into the hollow chamber profile, the fan running for a predeterminedtime span after deactivation of the printing or copying device.
 37. Asystem according to claim 31 in which the conveyor belt comprises aplastic belt with a specific volume resistance of between 10¹¹ and 10¹⁵Ωcm.
 38. A system according to claim 37 in which the conveyor belt isessentially comprised of polyvinylidenfluoride.
 39. A system accordingto claim 31 in which the recording medium is conveyed to the fixingdevice and then along a free transport section in which the recordingmedium can freely arch.
 40. A system according to claim 31 in which alength of the guided transport section is at least ⅓ a length of ashortest recording medium to be printed.
 41. A system according to claim31 in which a length of the guided transport section is between 100 mmand 210 mm.
 42. A system according to claim 39 in which a length of thefree transport section is at least ⅓ of a shortest recording medium tobe printed and is shorter than a length of the shortest recording mediumto be printed.
 43. A system according to claim 39 in which a length ofthe free transport section is between 80 mm and 130 mm.
 44. A systemaccording to claim 31 in which a speed with which the recording mediumis conveyed through the fixing device is between 97% and 100% of a speedwith which the recording medium is transported in the guided transportsection.
 45. A system according to claim 31 in which, at an end of theguided transport section, the transport band is guided around a rollerthat has a specific volume resistance of 10 ⁷ to 10 ⁹ Ωcm.
 46. A systemaccording to claim 45 in which the roller comprises silicon.
 47. Asystem according to claim 45 in which the roller comprises a driveroller.
 48. A system according to claim 31 with a discharge device todischarge toner located on the recording medium.
 49. A method fortransfer printing of an electrostatically charged toner image from anintermediate carrier of an electrographic printing or copying deviceonto a recording medium and for fixing of the transfer-printed tonerimage onto the recording medium, comprising the steps of: transportingthe recording medium lying on an electrostatically-chargeable conveyorbelt and adhering thereto due to electrostatic forces through a transferprinting region and subsequently along a guided transport section;conveying the recording medium to a fixing device; and arranging theguided transport section in a transport unit and arranging the fixingdevice in a fixing unit used independent of one another in the printingor copying device and which are removable, the fixing unit having atleast one wall designed as a hollow chamber profile and which hinders aheat transfer from the fixing unit to the transport unit.
 50. A methodaccording to claim 49 in which the hollow chamber profile has openingsthrough which air is drawn to cool the transport unit.
 51. A methodaccording to claim 50 in which air is taken up into the hollow chamberprofile from an environment of the conveyor belt.
 52. A method accordingto claim 50 in which air is taken up into the hollow chamber profile isfiltered with an ozone filter.
 53. A method according to claim 49 inwhich the conveyor belt is essentially comprised ofpolyvinylidenfluoride.
 54. A method according to claim 49 in which therecording medium is conveyed to the fixing device and then subsequentlyalong a free transport section in which the recording medium can freelyarch.
 55. A method according to claim 49 in which a length of the guidedtransport section is at least ⅓ of a length of a shortest recordingmedium to be printed.
 56. A method according to claim 49 in which alength of the guided transport section is between 100 mm and 210 mm. 57.A method according to claim 54 in which a length of the free transportsection is at least ⅓ of a shortest recording medium to be printed andis shorter than a length of the shortest recording medium to be printed.58. A method according to claim 54 in which a length of the freetransport section is between 80 mm and 130 mm.
 59. A method according toclaim 49 in which a speed with which the recording medium is conveyedthrough the fixing device is between 97% and 100% of a speed with whichthe recording medium is transported in the guided transport section. 60.A method according to claim 49 in which toner located on the recordingmedium is discharged with aid of a discharge device.
 61. A method fortransfer printing of an electrostatically charged toner image from anintermediate carrier of an electrographic printing or copying deviceonto a recording medium and for fixing of the transfer-printed tonerimage onto the recording medium, comprising the steps of: transportingthe recording medium lying on an electrostatically chargeable conveyorbelt and adhering thereto due to electrostatic forces through atransfer-printing region and subsequently along a guided transportsection; conveying the recording medium to a fixing device; andarranging the guided transport section in a transport unit and arrangingthe fixing device in a fixing unit, independent of one another in theprinting or copying device, the fixing unit having at least one walldesigned to hinder a heat transfer from the fixing unit to the transportunit.